Distribution of glycoconjugates in the optic vesicle and optic cup.

Lectin histochemical methods and immunohistochemical techniques have been utilized to investigate and partially characterize glycoconjugates in the developing eye. Peanut-lectin-binding sites associated with radial glial cells were found in the diencephalon. In the optic primordia, binding sites associated with radial glia were masked by terminal sialic acid, and only reacted with peanut lectin when pretreated with sialidase. This finding indicates that glycoconjugates associated with diencephalic radial glia contain terminal galactose-beta-(1----3)N-acetyl galactosamine, but glycoconjugates associated with radial glia in the optic primordia contain sialic acid----galactose-beta(1----3)N-acetyl galactosamine. The selective distribution of galactose, N-acetyl galactosamine and fucose associated with radial glial cells has also been demonstrated. We postulate that these distributions mediate the shaping of the developing eye.

Hypothalamic site of action for N-methyl-D-aspartate (NMDA) on LH secretion.

Excitatory amino acids have been shown to increase luteinizing hormone (LH) secretion following ventricular or systemic administration. In the present study we attempted to determine possible hypothalamic sites of action for the potent excitatory amino acid agonist, N-methyl-D-aspartate (NMDA). The ability of NMDA to enhance LH release was tested in male rats following infusion into the medial preoptic nucleus (MPO), anterior hypothalamic nucleus (AHY), ventromedial hypothalamic nucleus (VMH), and arcuate nucleus (ARC). In the MPO, infusion of 50 or 500 pmole NMDA increased pituitary LH secretion, resulting in a 2-7 fold increase in plasma LH. The 50 pmole dose was selected to test more caudal hypothalamic sites. Plasma LH levels were not affected following microinfusion of NMDA (50 pmole) into the AHY, VMH, and ARC. The present results indicate a regional specificity for NMDA in the enhancement of LH secretion. This regional specificity may reflect either a greater density of LHRH perikarya in the MPO or the presence of specific amino acid receptors on neuronal elements in the MPO, but not on neuronal elements in the other areas tested.

Tectal transplants into the occipital cortex of the newborn rat.

Embryonic day 15 rostral tectum (presumptive superior colliculus) was transplanted into the occipital cortex of newborn rats. One to two months later, the transplants were visualized and injected with either horseradish peroxidase (HRP) or wheat germ agglutinin conjugated with HRP (WGA/HRP). After the appropriate survival time and processing with either diaminobenzidine (DAB) or tetramethylbenzidine tetrahydrochloride (TMB), HRP-labelled pyramidal cells were found in layer V of the host ipsilateral occipital cortex. Thus, the occipitotectal connections are formed between host and graft despite the fact that the fibers must grow in a direction opposite to their normal course to reach the aberrantly positioned tectal graft.

Maintenance of transient occipitospinal axons in the rat.

A developmentally transient occipitospinal projection arising from the visual association cortex persists if a fetal tectum is transplanted to the spinal cord at birth and at the same time, the host tectum is removed. The pathway is not sustained if the transplant is placed in the cord without a tectal lesion or if the tectum alone is damaged. Thus the tectal transplant promotes the survival of normally transient occipitospinal axons as long as another regular target of these axons is removed.

Peripheral sensory nerve fibers that dichotomize to supply the brachium and the pericardium in the rat: a possible morphological explanation for referred cardiac pain?

Two fluorescent dyes, 'True Blue' and 'Diamidino Yellow' were injected, respectively, into the pericardial sac and into the medial brachial cutaneous nerve or subcutaneously into the medial side of the brachium. Double-labelling was observed in ipsilateral dorsal root ganglia neurons of spinal cord segments C8, T1 and T2, indicating that dichotomizing afferent fibers supply both the pericardium and the brachium. This finding provides a possible morphological explanation for referred cardiac pain.

The use of lead as an ionic tracer for investigating routes of passive fluid transfer.

Several inorganic ions, including lead, barium, silver, and thallium, have been tested as possible tracers for demonstrating fluid-accessible channels in functional epithelia at the ultrastructural level. The most useful of the ionic tracers examined was the lead (plumbous) ion, administered for short time intervals (less than 2 min) and "captured" with phosphate used as the buffer in the fixative. Passive fluid and ion-accessible channels of rat parotid salivary gland have been examined with this method. At short tracer infusion times (0.5-1.0 min), localization of the tracer was primarily extracellular, although intracellular deposits were observed in the following sites: smooth membrane-delimited endocytic vesicles of both epithelial and connective tissue cells, inner Golgi cisternae, and occasional cisternae of rough endoplastic reticulum. The lead tracer readily penetrated tight junctions between parotid acinar cells but rarely passed through the tight junctions between intercalated duct cells and did not penetrate junctions of striated duct cells. Fat cells observed in the stroma of this gland were the only cells that exhibited lead tracer in the cytosol, suggesting that the plasmalemma of this cell type is more permeable to exogenous ions than the plasmalemma of other cell types present in this gland.

Topographical representation of the peripheral nerve branches of the facial nucleus of the opossum: a study utilizing horseradish peroxidase.

The main facial nucleus of a marsupial, the North American opossum (Didelphis marsupialis virginiana), was subdivided into 6 portions by localizing HRP-positive neurons after injecting all muscles by each major peripheral motor branch of the facial nerve. In the medial lobe of this dumbbell-shaped nucleus the caudal auricular nerve, rostral auricular ramus and cervical ramus were represented dorsomedially, dorsolaterally and ventrally, respectively. The lateral lobe contained zygomatic ramus cells dorsomedially, marginal mandibular ramus cells ventromedially and buccal rami cells laterally. The cells supplying the caudal digastric muscle were in the accessory facial nucleus. Thus, even though the facial nucleus of the opossum lacks distinct ramal subdivisions in Nissl preparations, such are evident after HRP labeling.

Morphology and cytochemistry of acinar secretory granules in normal and isoproterenol-treated rat submandibular glands.

Several fixation procedures have been utilized in a fine-structural study of rat submandibular glands with the aim of correlating the morphology of granule substructure with its composition. Procedures included fixation with aldehyde in a variety of buffers, with or without fixation additives such as tannic acid or calcium chloride. Both immersion and perfusion fixation studies were performed. Osmium tetroxide postfixed tissue was compared with non-postfixed tissue. Thin sections were stained for carbohydrate-containing constituents by either periodic acid-thiocarbohydrazide-silver proteinate or tannic acid-ferric chloride sequences. The morphology and cytochemistry of acinar secretory granules were highly dependent upon the fixation procedure utilized. In postfixed tissue, fine filaments and vesicles were the major granule constituents. Filaments often aggregated into fibrils in fixatives containing phosphate buffer or calcium, whereas vesicles were prominent with fixatives containing collidine buffer. Tannic acid, as a fixation additive, imparted enhanced density to the peripheral rim of aggregated filaments. If post fixation was eliminated, an amorphous meshlike material was the major granule component. This stained readily with methods for carbohydrate whereas the granules of post-osmicated tissue did not. Following chronic isoproterenol treatment the degree of filament aggregation in postfixed tissue was augmented, and this corresponded to an increase in amount of material stainable for carbohydrate in non-post-osmicated tissue.

Functional localization and cortical architecture in the nine-banded armadilli (Dasypus novemcinctus mexicanus).

A functional map of the armadillo neocortex was produced by cortical stimulation and recording evoked potentials following somatic, auditory and visual stimuli. The results obtained were then correlated with the cortical architecture as revealed by Nissl, Golgi and myelin-stained sections. Cortex rostral to the supraorbital sulcus has a wide layer IV and is mostly silent, except for a motor eye field and a part of the tongue sensory region in its caudal part. Two types of motor-sensory cortex are present caudal to the supraorbital sulcus. Postsupraorbital I is mostly motor and has prominent pyramidal layers. Layer V is particularly well developed and in rostral sections its superficial zone is broken up into clusters similar to the solid "barrels" seen in layer IV of other species. Postsupraorbital II has less prominent pyramidal layers and layers II and III are organized into clusters. This region corresponds to the sensory area for the limbs and trunk and the partially overlapping (surface recordings) sensory and motor areas for head, snout and tongue. Digits and limbs are rostral to the trunk representation in both the sensory and motor "homunculi." Even though surface recording was employed, potentials evoked by visual stimuli could only be recorded from a small caudal area with a very thin layer IV. Although striate and peristriate areas appear similar in Nissl stained preparations, they can be readily differentiated in Weil stained sections. The stellate character of neurons in layer IV of the visual cortex is particularly apparent in Golgi material. Auditory evoked surface potentials were recorded from a broad oval region in the caudal lateral cortex which has a wide layer IV and aggregates of neurons in layers II and III. A Weil stain demonstrates inner and outer bands of Baillarger in this same region. The presumptive insular cortex is electrically silent to sensory stimulation and presents as a narrow band just dorsal to the rhinal fissure with indefinite cell lamination and little myelin.